An acoustic instrument produces sound and music that originates from the material, structure and artisanship of the instrument itself. An acoustic instrument, in the hands of an experienced player, can create sound and music with high expressive qualities, in terms of texture, timbre, articulation and dynamics in the music parlance, or in terms of their expressed nuance, sophistication, emotion or even inspiration as appreciated by those who love music.
On the other hand, a digital instrument produces sound and music that are retrieved and synthesized from a digital library of sound and music. Despite decades of efforts, a digital instrument has not been able to retain much of the expressive qualities of an acoustic instrument. It is certainly true that music created by digital instruments can be enhanced with many effects. For example, MIDI data can be used to add digital effects to the sounds played, such as reverb, chorus, delay and tremolo. However, a button may still need to be pushed each time an effect is to be activated or deactivated. These “effects” cannot match the expressive qualities created by a professional with an acoustic instrument, when various techniques can be employed at once and at will to express the interpretation of the music by the professional. For example, it is therefore difficult to allow a vibrato or a portamento at once and at will, when an electronic piano is played in the violin mode.
To enhance the expressive qualities of a digital keyboard instrument, one approach has been to place 2, 3 or even more sensors under each key. The velocity of the key depressions are captured and corrected in complex ways to produce a sound of the key that incorporates the speed and force of the key depression. Most of the time a direct proportional relationship between the velocity and the amplitude of the note is adopted. The enhancement of expressive quality of this approach is still fundamentally limited by the number of data points being collected for each key depression action.
People have also sought to increase the amount of data points being collected by using different kind of sensors. Hall-effect sensor, photoelectric sensor, piezoelectric sensor, or pressure sensor have all been tried to generate a more continuous or analogue output that captures better the dynamics of a single keystroke by a person. In all of these efforts, the result of the key movements generate by a figure touch action is captured with finer granularity, but the dynamic movement of the finger itself is not directly captured. One limitation is that no prior art to date has been able to capture the motion of a finger when the finger is approaching or leaving the key but is actually not touching the key. Another limitation is that no prior art to date has been able to capture the motion of a finger when the finger is touching a space between the physical boundaries of two sensors. With most digital keyboards marketed with the functionality to play a myriad of instrument sound including piano and stringed instruments, these limitations produces some loss of musical expressions when the keyboard is played as a keyboard instrument, and severe loss of musical expressions when the keyboard is played as a stringed instrument. Moreover, these limitations do not help to enable a digital instrument to become even more seamlessly expressive than an acoustic instrument.
Simply put, a seamless integration of producing a note through touching a key or a string and making the note expressive through a variety of techniques comes very naturally for an acoustic instrument; nonetheless, such seamless integration is yet to be enabled for a digital instrument, with one barrier being the inability of prior art to capture the dynamics and sophistication of the finger motion directly. Therefore, there is a need to capture directly the unique dynamics of the touch action by an experienced player of the musical instrument, so as to enable a digital instrument to generate a music piece that is as seamlessly expressive as an acoustic instrument.